International Publication No. 2011/125376 and United States Patent Application Publication No. 2013/0011183 (the content of which is incorporated herein by reference in its entirety) disclose a dissimilar-material welded structure formed by welding dissimilar materials, such as a carbon steel material and an aluminum material, by utilizing friction stir welding. In this dissimilar-material welded structure, with respect to joint portions to be welded by using a welding probe, a joint portion having a smaller height of a plastic flow region is located at one side of the aluminum material and a joint portion having a larger height of a plastic flow region is located at the other side of the aluminum material.